Current electric vehicles, in particular hybrid vehicles, employ recuperative and/or regenerative braking techniques to utilize a maximum amount of kinetic energy of the vehicle by using the electric engine as a generator to recharge a traction battery of the vehicle and/or to power equipment of the vehicle during a braking maneuver. By employing regenerative braking, the range of electric vehicles may be increased and the fuel consumption and thus the CO2 emissions may be reduced significantly, in particular in urban traffic situations involving frequent braking and/or acceleration.
In case of conventional braking systems, normally both a mechanical brake (e.g. a vacuum pressure actuated friction brake for braking the wheels) and a regenerative brake operate in parallel, that is, simultaneously, such that a less than optimal amount of energy may actually be recuperated. To improve on such conventional systems, cooperative braking systems have been introduced. These systems provide a direct distribution of braking power to a mechanical brake and an e-machine brake depending on the specific driving situation. For example, the braking power of the e-machine may be used in regenerative mode under average driving conditions. However, the available e-machine power may vary based on factors such as speed and battery state of charge. Accordingly, in specific cases and/or for specific states of charge of the battery, the friction brake may be used to support and/or substitute the regenerative braking, e.g. for rapid deceleration, at low speed and/or in stationary situations.
Such systems are particularly useful in case of electric engines with high power output. However, in some use cases, e.g. mild hybrids or other hybrids with small electric engines, regenerative braking may be limited. In these and other cases the above solutions may be over-engineered and/or too costly.